The invention is based on a device and a method for monitoring undercarriage components of rail vehicles for faults.
The monitoring systems for undercarriages are becoming increasingly important in rail vehicle transportation. On the one hand, for safety reasons, these monitoring systems are required normatively and in guidelines. Examples of this are the following systems which are required throughout Europe by the TSI (Technical Specification for Interoperability—Official Journal of the European Community) for high speed trains:                On-board systems for detecting derailing,        On-board systems for hot box detection and/or for detecting damage to bearings, and        On-board systems for detecting instability and/or defective dampers.        
On the other hand, the use of undercarriage monitoring systems for the diagnosis and early detection of damaged components, critical states and other faults in order to achieve early and status-oriented maintenance occurs. Objectives here are shorter downtimes, better utilization of components and therefore reduction of costs.
For example, in the ICE a system for detecting unstable running is used, and in relatively new automatic underground railway systems a system for detecting derailing is used. These systems have in common the fact that, in terms of function, they are constructed and act independently. Each of these systems uses dedicated sensors.
For instability detection, one or more sensors are usually mounted on the bogie frame, which sensors measure the lateral acceleration (in the transverse direction with respect to the direction of travel x) in a specific frequency range and generate an alarm message when their limiting values are exceeded.
DE 101 45 433 C2 and EP 1 317 369 describe a method and a device for monitoring components of a rail vehicle for faults, which method and device are also based on the measurement of acceleration values and are mounted on lateral damper brackets attached to the wagon body. The detection direction of the acceleration pickup is parallel to the direction of travel there.
An example of a method and a device for detecting derailing is described in DE 199 53 677. Here, measurement signals of an acceleration sensor which is arranged on an axle bearing are evaluated directly. The measured acceleration values are integrated twice and compared with a limiting value. The simple acceleration sensor has a detection direction extending in the direction of the vertical axis (z direction) of the rail vehicle. However, according to the document, acceleration sensors which simultaneously have detection directions in the direction of travel (x direction), in the transverse direction with respect to the direction of travel (y direction) and in the direction of the vertical axis (z direction) can also be used. Such an acceleration pickup is what is referred to as a multiple pickup, i.e. it is actually composed of at least two, here three acceleration pickups, each of which measures in one detection direction.
The problem with these safety-related monitoring devices is to ensure the functionality capability of the acceleration sensors which, depending on the safety level, cannot be guaranteed with a high degree of fail safety or detection of failures. FIG. 8 is a schematic view of the design and the function of a device for monitoring undercarriage components of rail vehicles for faults, which comprises the following:                an acceleration sensor including attachment and integrated amplifier electronics and adaptation electronics,        signal conditioning electronics and evaluation electronics including a supply device for the acceleration sensor,        transmission lines for transmitting the signals of the acceleration sensor to the evaluation electronics, and        transmission lines for supplying power to the acceleration sensor.        
The functional capability of many components of the measurement chain shown in FIG. 8 can be tested during operation by means of test functions or circuits. It is therefore possible, for example, to detect a break in the transmission line by feeding in an offset voltage (medium voltage) or feeding a constant current to the acceleration sensor. A break in the line can then be detected from a change in the offset voltage or in the constant current.
On the other hand, testing the acceleration sensors themselves is problematic. In order to detect that the acceleration sensor is still functioning and is supplying a measurement signal precisely according to its specification, it is necessary to apply a defined acceleration signal to it. For this purpose, the acceleration sensor has to be dismounted and then mounted on a calibrated test bench (shaker), which constitutes a large amount of expenditure against the backdrop that acceleration sensors are often arranged in installation spaces which are difficult to access, such as bogies of rail vehicles. Furthermore, during the dismounting and remounting it is not possible to exclude the possibility of damage occurring to the sensor or of incorrect mounting occurring.
Another possibility is provided by sensors with a dedicated self testing device. In such sensors, the sensor element is excited by an additional integrated device. If the sensor supplies an anticipated signal it is intact. Such self testing devices are used, for example, in airbag sensors in motor vehicles. However, such a self testing device is not available for every type of sensor or every size of sensor and makes the sensor more expensive.
In order to avoid sensor tests on disinstalled sensors or self testing devices it is possible to provide acceleration sensors redundantly and to detect a failure or a malfunction of a sensor by comparing the two sensor signals for plausibility. However, this also requires a relatively high degree of technical expenditure and therefore increases costs.